1. Field of the Invention
The present invention relates to an apparatus for generating a pilot beacon of a Base Station (BS) in a mobile communication system. More particularly, the present invention relates to an apparatus for generating a pilot beacon, to be used for performing handover of a Mobile Station (MS), in a BS supporting two types of communication systems.
2. Description of the Related Art
In general, when a normal Base Station (BS) operating multiple Frequency Assignments (FAs) is located adjacent to a compact BS operating a smaller number of FAs than the normal BS, calls may frequently drop, due to different FAs between the two BSs. To provide seamless call without dropping calls, the compact BS transmits a beacon signal, i.e., the same virtual radio frequency as an FA used in the normal BS, so as to induce a handover of a Mobile Station (MS).
FIG. 1 illustrates an operation of generating a beacon in a compact Base Station (BS) for a Frequency Assignment (FA) of a normal BS. For example, as shown in FIG. 1, when a normal BS 100 supports beacons F1 to F5 and a compact BS 110 supports only one beacon F1, the compact BS transmits the beacons F2 to F5 in turn, so as to induce a handover of an MS receiving a service from the BS 100. In this case, when the compact BS transmits multiple beacons in turn as described above, these beacons are called hopping pilot beacons.
FIG. 2 is a timing diagram illustrating a conventional hopping pilot beacon, Referring to FIG. 2, three parameters are defined for a hopping pilot beacon 207 according to the Interim Standard (IS)-2000, and the parameters are a NGHBR_TX_PERIOD 201 for indicating a period of a pilot beacon transmission window, a NGHBR_TX_DURATION 203 for indicating a pilot beacon transmission duration, and a MGHBR_TX_OFFSET 205 for determining a transmission start position of a pilot beacon based on a first transmission window. The three parameters allow an MS to recognize the hopping pilot beacon through use of a General Neighbor List Message (GNLM) of a neighbor BS.
The conventional compact BS uses a signal copy method to transmit the pilot beacon. FIG. 3 is block diagram of an apparatus for generating a beacon by using a signal copy method in a conventional compact BS and FIG. 4 illustrates a beacon output according to a control signal of a hopping pilot beacon in a conventional signal copy method. Referring to FIG. 3, the BS using the signal copy method consists of a main system 300 for supporting a main FA within the BS and a beacon subsystem 310 for generating and transmitting a beacon. Thus, the beacon subsystem 310 copies a transmission signal currently being operated by a main FA in an Intermediate Frequency (IF) stage or a Radio Frequency (RF) stage, and shifts its frequency into a desired frequency. Thereafter, as illustrated in FIG. 4, the beacon subsystem 310 transmits a frequency-shifted signal by controlling output timing of the frequency-shifted signal.
Voice-based CDMA2000 1x and data-based CDMA EVolution Data Optimized (EV-DO) coexist in current Code Division Multiple Access (CDMA) mobile communication systems. To support this coexistence, a CDMA2000 1x BS and a CDMA EV-DO BS are installed together, or a BS supporting both CDMA2000 1x and CDMA EV-DO is newly installed. Since use of compact BSs has become a trend, pico/femto BSs supporting both CDMA2000 1x and CDMA EV-DO are being newly installed. FIG. 5 illustrates an operation of generating beacons for FAs of two types of systems in a conventional BS supporting both a CDMA2000 1x system and a CDMA EV-DO system. As illustrated in FIG. 5, for a case where an MS receiving a service from a macro BS supporting multi-channel CDMA2000 1x and CDMA EV-DO performs a handover to a pico/femto BS, the pico/femto BS must generate a hopping pilot beacon for both CDMA2000 1x and CDMA EV-DO.
FIG. 6 is a block diagram illustrating an apparatus for generating beacons for FAs of two types of systems in a conventional BS supporting both a CDMA2000 1x system and a CDMA EV-DO system. As illustrated in FIG. 6, to generate the hopping pilot beacon, the BS supporting CDMA2000 1x and CDMA EV-DO must include subsystems 601 and 603 for CDMA2000 1x and CDMA EV-DO systems, respectively. However, since a power amplifier module and a transmitter included in each subsystem are expensive components, employing each of the subsystems is not cost effective.